Abstract: Because the climate change is considered caused by the greenhouse gases added to the atmosphere since the beginning of the industrial revolution, developed countries are held responsible for the harmful effects of climate change which generally hit the poor countries first. World efforts so far resulted mainly in coordinated attempts to address climate change, primarily through the nationally determined contributions that are updated at the regular conferences of the parties to the UNFCCC. However, decisions on providing help by the reach to the poor nations sounds like voluntary aid rather than a liability to compensate for unequal rights for industrial growth. This becomes an overburden for the industry when solving its own net-zero emission goal, in which the usual cost-benefit analysis makes the so-called net-zero emissions equation practically unsolvable for the near- and mid-term. The report also deals with the efforts by the industry to meet its assigned net-zero goal for the long-term.

КОРИШЋЕЊЕ ПРИРОДНОГ ГАСА У СРБИЈИ Резиме Србија је релативно касно почела са коришћењем природног гаса. Но и поред тога развој програма гасификације правилно је одређен и са успехом се спроводи, али релативно споро. Србија нема довољне производне капацитете и количине природног гаса за сопствене потребе и мора да се ослони на увоз. Програм гасификације Србије усмерен је на коришћење природног гаса у индустријској и широкој потрошњи, као и за производњу електричне енергије у когенерационом постројењима. Такође, важно је истражити, због смањења загађења околине, могућност коришћења природног гаса за погон моторних возила, као и за неке друге технолошке процесе. Нагли раст цена природног гаса на светском тржишту и ограничене могућности снабдевања, захтевају посебне услове и припреме за његову набавку и коришћење. Разне понуде снабдевања Србије из неких других извора, или снабдевања течним природним гасом интересантне су и треба их пажљиво размотрити. У раду су приказане могућности примене и коришћења природног гаса у индустрији, комуналној и широкој потрошњи, у комбинованим паро-гасним постројењима као и обезбеђење потребних количина за његову употребу. Abstract Serbia started using natural gas relatively late. Nevertheless, the development of the gasification program has been correctly determined and is being implemented successfully, but relatively slowly. Serbia does not have sufficient production capacities and quantities of natural gas for its own needs and must rely on imports. Serbia's gasification program is focused on the use of natural gas in industrial and mass consumption, as well as on the production of electricity in cogeneration plants. Also, it is important to investigate, due to the reduction of environmental pollution, the possibility of using natural gas to drive motor vehicles, as well as for some other technological processes. The sharp rise in the price of natural gas on the world market and the limited possibilities of supply require special conditions and preparations for its procurement and use. Various offers of supplies to Serbia from some other sources, or supplies of liquefied natural gas, are interesting and should be carefully considered. The paper presents the possibilities of application and use of natural gas in industry, utilities and general consumption, in combined steam-gas plants, as well as the provision of the necessary quantities for its use.

CO2 emissions induced climate change that started the transition from traditional fossil fuels to renewables. Energiewende German say. Coal is hardly viewed as part of the energy mix that is climate-friendly. Serbia used a lot of Black gold, and it was the backbone of the country’s energy system. But times are changing. We have choice either to adopt or to have problems. Serbia is part of the Energy Community and in EU accession talks. Serbia as a part of the European electricity network is not independent in energy policies. In case of electricity independence, then situations that occured in Texas during the winter storm Uri could repeat and lead to serious problems in electricity supply and stability. Power plants in Serbia are not obliged to pay for CO2 emission, but this can change. Trend in the world is that coal power plants report impairments in their final yearly reports. Great number of coal power plants is closed. One example is Moorburg power plant that is youngest and one of the most efficient ones. Owner of the Moorburg is Swedish Vattenfall that was developing its own solution for CCS tested in Schwarze pumpe power plant. But it decided not to apply CCS but to follow path of decarbonisation and move to wind power and hydrogen storage. Serbia faces tough choices. On the one hand there is a need for energy supply security and on the other are strict rules accepted for power plants in frame of Energy Community. In the world a lot of coal power projects has been canceled, but in Serbia one block is being developed, namely Kostolac B3. One option is to invest more into renewables and into their research so that there are more Made in Serbia products. Coal power plants can serve as a energy storage. There are more then a few paths that can be implemented. In this case there will be no more combustion, but almost all equipment would be in use. That means that people working in these power plants would not lose their jobs and their acquired skills would be in full use. On parallel path Serbian CCS solution should be developed. Our scientists have proven their expertise on SO2 removal project that unfortunately did not pass from succesful pilot to demostration phase. Future is in electrification, so heating should be also electricity oriented. Like for example Berlin electricity boiler district heating, or even beter example is Esbjerg where heating is going to be done from 2023 on by heating pumps that use wind electricity and waste heat from sea water. All in all decarbonisation and electrification are the keywords of the future. Now is the time to develop new solutions in these fields as market for these products exists and is growing. Not to forget funding for these purposes is available.

In electricity generating systems with high penetration of i-RES, the ability of change the power on demand has increasing importance. Following recently published Ulrich’s and Schiffer's approach with assured capacity; in this paper is defined term total assured capacity and is further applied together with dispatchability indicator and possible duration of load change to indicate dispatchability of Serbian power system (EPS). The results of the performed analyses are presented. Total assured capacity appears as very sensitive indicator and its numerical value changes significantly if, in the hypothetical case, one technology e.g., lignite fired power plants have to be substituted with the other technology like wind turbines. An overview of participation different technologies for electricity generation within Serbian power system is presented together with a comparison with German power system. Numerical values of dispatchability factors for EPS’s fossil fueled power plants are presented and discussed. It is underlined the necessity of a specific project study for EPS’s power plants to be performed aimed to define real technology possibilities, limitations that are conditioned by the quality of lignite, as well as the cost increase that arise in satisfying the needs to change the power on demand in conditions determined by hypothetical increase of i-RES electricity generation.

Competitiveness of an energy technology is considered as ability of the energy technology to compete other energy technologies. In the paper is presented a simple procedure for competitiveness assessment of energy technologies in post transition. The idea is to define a frame of overall energy quantity that is needed within predefined time span and to compare effects of different energy technologies in the case of their application within the frame. For the purpose of the comparison, a special 3Ee-t indicator is developed. Numerical value of the indicator indicate competitiveness of each energy technology selected for application within energy-time frame. The procedure is exemplified with competitiveness assessment of seven different energy technologies, i.e. existing technologies of hard coal and lignite fired power plants, advanced technologies of hard coal and lignite fired power plants with CCS technologies, natural gas fired CCGTs, nuclear power plants and wind turbines. Obtained results are presented and discussed. The results point out that the most competitive is nuclear power plants technology, followed by natural gas fired combined cycle gas turbines technology. The energy-time frame procedure can be applied and for competitiveness assessment of energy technologies during the period after technology transition, the period that can be named as post-transition.

The examples presented in this paper are in contrast to prevailing fossil fuel addiction practices. Unfortunately, it is always easier to follow business as usual then to make U turns/drastic changes. These PPMs of CO2 in atmosphere rising every day do not present clear and imminent danger to many decision makers. Due to these failing policies, we are reaching tipping points fast, when the changes in atmosphere are becoming exponential and irreversible. These lessons are result of: out of the box thinking, fossil fuel freedom fighting, perfect combination of imagination and engineering, moonshots, groundbreaking solutions, game changers, "walk the talk approach", saturation with empty promises, finding and applying the missing puzzles, decarbonization at the right moment, not waiting for disasters to strike, for some next Uri-like winter storm, next stronger then Katrina hurricane, billion dollar in damages flooding, or devastating droughts inducing continent-wide famines. This paper describes selected occupants of hall of energy sustainability fame, where unintentionally certainly some solutions, companies or countries are missed. So, this paper virtually visits: Esbjerg (DK), Dronninglund (DK), Heerlen (NL), takes us to desert (AU), mentions some innovative machines like HOFIM (DE), some innovative concepts like Virtual power plants (US), highlights the strategy and results of one company Vattenfall (SE) and one country Chile, talks how air that is all around us is going to be used as energy storage (ES), and even is being used as a motive fluid in Dearman engine where no fuel is combusted (UK).

In light of the post-Covid pandemic and the Ukraine crisis, electricity and natural gas have become goods in high demand and prices. As a result, electricity and natural gas prices reached their highest level, and trends show there is still uncertainty in price forecasting, which leads us to conclude that the value of energy saved by applying energy efficiency measures becomes much higher than the value of primary energy sources themselves. Therefore, the concept of energy efficiency becomes a keyword in every speech to the public. Since the first energy crisis back in the 1970’s energy efficiency has been introduced as a critical term in solving the problem of limitations of fossil fuel sources. The second energy crisis accelerated the introduction of new, more energy-efficient technologies and renewable energy sources. Today, we have new challenges – an unfinished energy transition and an artificially induced lack of energy sources like natural gas. The Republic of Serbia is among the European countries with the highest energy intensity and is significantly dependent on fossil fuels, especially coal. The energy intensity of Serbia (ratio between primary energy consumption and the GDP) has been consistently higher than the EU member states and other non-EU countries of Europe (2 to 3 times higher than in the neighboring EU countries and up to 4 times higher than EU-15). In 2013 Serbia introduced an energy management system (EnMenS). Through this system, significant final energy consumers are recognized and obliged by Energy Efficiency Law to implement energy efficiency measures to reduce energy consumption by at least 1% per annum. However, EnMenS do not recognize “small” energy consumers, where small to medium size enterprises (SMEs) are categorized. The SMEs sector in the Republic of Serbia accounted for 27.3 % of total active enterprises, employing 46.2 % of employees in the non-financial sector and participating with 43.2 % in the GDP of the non-financial sector. However, the distribution of the number of companies, employees, and their economic activity is highly uneven, where the Belgrade region “carries” 45.8 % of activities in the SME sector, Vojvodina 25.9 %, Šumadija and Western Serbia 18.4 % and Southern and Eastern Serbia 9.8 %. SMEs are primarily concentrated in labor-intensive and service activities - manufacturing, wholesale and retail trade, construction, and transport. The manufacturing industry dominates within the tradable sector - 17.1 % of companies, 28 % of employees, 21.1 % of turnover, and 24.7 % of GDP. It is dominated by sectors of lower complexity and lower productivity (labor and resource-intensive activities). During 2021 energy audits in ten selected SMEs of the production sector were performed. The primary purpose was to support SMEs in improving the efficient use of energy and reducing costs and emissions, directly contributing to the competitiveness of the Serbian industrial sector and awareness raising in the energy efficiency field. However, although there is a high potential for energy savings in Serbian SMEs, there are several barriers: - SMEs are not aware of energy-saving opportunities; - SMEs do not have the human and financial resources to analyze and explore energy-saving opportunities; - SMEs recognize the direct cost benefits, but energy-saving measures categorize as high-cost and high-risk activities. This paper presents the result of performed energy audits showing that in current conditions, energy efficiency is a crucial driver for the sustainable growth of SMEs in Serbia’s industrial sector.

• Tipovi Toplotnih Pumpi: prema vrsti izvora/ponora, tehnologiji rada i načinu delovanja važno za pravilan izbor • COP: osnove i proračun za različite temperature izvora i ponora i potrebne kapacitete sa osvrtom na dvostepene TP • Smanjenje temperature toplotnog ponora značajno utiče na povećanje efikasnosti (COP) • Dvostepena TP ima 5 do 20% veći COP ali je komplikovanija i znatno skuplja i investiciono i u pogledu održavanja • Povećanje temperature toplotnog izvora značajno utiče na povećanje COP a • Analiziran je uticaj temperatura izvora i ponora na ROI za konkretan slučaj (i pretpostavljene parametre) smanjenje stepena sabijanja dovodi do 15 34% boljeg ROI a produžavanje korišćenja TP tokom cele godine za niskotemperaturske potrebe značajno smanjuje ROI • Prikazan je uticaj izbora konfiguracije sistema u smislu paralelna/redna veza TP na povećanje COP kada može redna veza je bolja • Analiziran je uticaj TP na smanjenje emisije CO2 zbog lošeg EGIF kod nas je granica kada TP ima emisiju istu kao gasni kotao na COP=3,3 očekuje se smanjenje EGIF sa većom upotrebom OIE • Dati su realni primeri primene TP za daljinsko grejanje i u procesnoj industriji i ukazano je na neke pravce razvoja ove tehnologije (rotacioni kompresor, voda kao rashladni fluid...).

In energy-intensive industries such as foundries, ironworks, chemical plants, refineries, etc. significant amounts of waste heat are generated in the form of cooling water, with the temperature usually in the range of 25 to 40°C. In cases where the waste heat is of a low temperature, insufficient for direct use, it can be used rationally by applying a heat pump that uses low-potential waste heat from the industrial process as a heat source, for the preparation of hot water for heating, sanitary hot water, technological hot water consumers or some other purpose. This paper presents the results of techno-economic analysis on the example of the application of high-temperature heat pumps for the utilization of waste heat in industry. In the paper several different sources of waste heat with different characteristics in terms of flow rate, water temperature and operation mode are analyzed. The results of the analysis showed that the application of heat pumps with a nominal heat output of 295 and 2x390 kW, at a temperature regime of 80/30°C and a COP of 3 is justified, with a simple payback period of the investment at approximately 4 years.

Pri preradi nafte i naftnih derivata u rafinerijama za potrebe proizvodnih pogona i pomoćnih postrojenja troši se relativno velika količina toplotne energije. Njena potrošnja se može smanjiti primenom različitih tehničko-tehnoloških rešenja i organizacionih mera. Jedno od najčešće primenjivanih rešenja je korišćenje otpadne toplote koja se produkuje u energetskim i procesnim rafinerijskim postrojenjima. Korišćenje otpadne toplote koja nastaje pri preradi nafte i naftnih derivata može se u značajnoj meri uticati na smanjenje potrošnje toplotne energije prilikom odvijanja proizvodnog procesa u rafinerijama. U radu su prezentovana iskustva i konkretni rezultati koji se postižu korišćenjem otpadne toplote u rafinerijama. Korišćenjem otpadne toplote smanjuje se potrošnja goriva za proizvodnju toplotne energije, a ujedno i količina gasova koji se emituju u atmosferu.

Циљ рада је представљање неколико различитих метода сушења дрвета и анализа њихових перформанси. Посебан акценат анализе је на енергетским перформансама, али је урађена и економска анализа. Уводни део рада се бави општом тематиком сушења дрвета, где су дефинисани основни појмови везани за влагу у дрвету, сушење, принцип рада неколико начина сушења, као и неке неконвенционалне мере за унапређење процеса сушења. Анализа је примењена на две врсте дрвета (буква и бор) дебљина 24 mm и 50 mm. Један од битних показатеља енергетске ефикасности сушења је “SMER” (eng. specific moisture extraction rate), који представља однос масе издвојене влаге из дрвета, изражене у kg и укупно искоришћене енергије за процес изражене у kWh. Сушење дрвета у атмосферским условима (природно сушење) има велику предност у томе што је у енергетском смислу готово „бесплатно“, али и велике недостатке у погледу ограничења минимално достижне влажности (20-30%) и што сам процес дуго траје (80 до 300 дана у поређењу са периодом од неколико дана до неколико недеља у случају сушења у сушари). У анализираним процесима сушења, задата крајња влажност дрвета је 10%, па самим тим процес природног сушења ни не би могао до краја да испуни задатак. Због тога је природно сушење за сваку од наведених варијанти анализирано као опција за фазу сушења која претходи сушењу у сушари, односно анализирана је корист смањивања почетне влажности са 64% на 30% уз све наведене недостатке. Анализирано је неколико различитих метода сушења обе врсте дрвета, обе дебљине и то у конвенционалној сушари коришћењем огревног дрвета, природног гаса и пелета као погонских горива, са претходним природним сушењем и без њега, као и у сушари са топлотном пумпом са претходним природним сушењем и без њега. Сваки процес сушења се одвија у 4 фазе: загревања, активног сушења, изједначавања и кондиционирања. Анализирани су параметри за сваку од фаза и за сваки наведени случај. На крају, упоредно су анализирани следећи резултати: укупно утрошена енергија за један циклус сушења за сваку од варијанти, јединични трошкови набавке енергената потребних за производњу једног m3 осушене грађе, удео трошкова енергетике у укупним производним трошковима, “SMER” коефицијент за сваку од варијанти, као и остварене добити у периоду од 1, 2 и 5 година рада постројења. Резултати су показали да је са аспекта коришћења енергије најнеповољније дрво букве дебљине 50 mm сушено у конвенционалној сушари са огревним дрветом као погонским горивом, а најповољније сушење бора дебљине 24 mm у сушари са топлотном пумпом са претходним природним сушењем. Са аспекта јединичних трошкова за набавку енергената за сушење је најнеповољније сушење дрвета букве дебљине 50 mm са пелетом као погонским горивом, а најповољније сушење бора дебљине 24 mm у конвенционалној сушари са природним гасом као погонским горивом, са претходним природним сушењем. Када се упоређује “SMER” коефицијент, сушаре са топлотном пумпом имају изражену предност у односу на конвенционалне сушаре. Анализом остварене добити у пословању, сушење у сушари са претходним природним сушењем у првој години пословања даје најлошије резултате, али после две, а нарочито после 5 година пословања има евидентну предност у односу на методе без претходног природног сушења. The goal of paper is to present several different methods of wood drying and their performance analysis. The emphasis is on performance in terms of energy usage, but work also contains financial analysis. First part of work contains general information about wood drying including moisture in wood, drying process, several different drying methods working principle, and some unconventional measures used to improve drying process. Analysis is applied on two different wood types (beech and pine), combining two different board thickness (24 mm and 50 mm). One of the best indicators of wood drying performance is “SMER” (specific moisture extraction rate) which represents ratio of removed moisture mass expressed in kg to used energy expressed in kWh. Drying wood in open air (natural air drying) has a big advantage in being almost “free” in terms of energy consumption, but it also has big flaws regarding minimal achievable moisture content (20 – 30%), and long drying periods (80 to 300 days compared to several days to several weeks of kiln drying time). In analysed cases, final moisture content is set to 10%, which is unachievable by natural drying. For that reason, natural pre-drying (wood is dried naturally before kiln drying which lowered initial moisture content from 64% to 30%) is analysed as an option to all variations, with all its flaws. Conventional kiln drying cases were analysed using firewood, natural gas, and wood pellet as fuel, with and without natural pre-drying. Also, cases with heat pump assisted kiln were analysed with and without natural pre-drying. Every drying process is divided in 4 phases: initial heating, active drying, moisture equalising and conditioning. Important parameters for each phase and for each case were analysed. Finally comparative results for each of the cases were shown including: gross consumed energy for one drying cycle, unit energy cost necessary for producing one cubic meter of final product, share of energy cost in overall production cost, SMER for each case, and profit in 1-, 2-, and 5-years period. Result have shown that in terms of energy usage most demanding is 50 mm thick beech drying in conventional kiln using firewood, and least demanding is 24 mm pine heat pump assisted drying with natural pre-drying. Comparation of SMER for each case has shown clear advantage of heat pump assisted drying methods compared to conventional kiln drying. Results of profit analysis have shown big disadvantage of pre-dried methods in the first year of running, but also a big advantage in second and especially fifth year of running.

The aim of this experimental research is to confirm the correctness of the proposed methodology for optimizing atmospheric gas burner Also, the burner will be tested in real conditions. The object of this experimental optimization is a typical modern atmospheric gas burner for households (required heat output for average households ranges from 8 to 12 kW) to which the proposed methodology will be applied in order to optimize its design characteristics and performance with a goal to obtain energy efficient and an environmentally friendly device.

The set of measurements were performed on an industrial air compressor, with a nominal power of 30 kW. Based on the measured values, an analysis of the working parameters of the air compression system was performed. The measured parameters are electrical power, temperature of cooling and compressed air and volumetric flow rate of cooling air. Based on the measured values, an assessment of system efficiency parameters, and a comparison of parameters with similar systems was performed. After analyzing the system parameters, the potential measures for improving the energy efficiency of the air compressed system are listed. The following improvement measure was analyzed in detail: installation of a compact plate heat exchanger (working medium - water, oil) for cooling heated oil and simultaneously heating sanitary water. This measure reduces annual costs by 1.050 KM and reduces emissions by 5 tCO2/a. Therefore, the introduction of this measure will improve the system's energy indicators and will results in the reduction of the energy consumption and energy costs.

Energetski pretvarači se sve češće koriste usled povećanih potreba za integracijom obnovljivih izvora energije u elektroenergetski sistem sa ciljem njegovog decentralizovanja. Takođe je učestala njihova upotreba i u industriji u regulisanim elektromotornim pogonima, u cilju povećanja energetske efikasnosti i realizacije složenih zahteva proizvodnih procesa. Kao posledica, javljaju se novi problemi stabilnosti mreže, kvaliteta napona, izobličenja talasnog oblika stuje i faktora korisnog dejstva. Metode za otklanjanje nekih od navedenih nedostataka zasnivaju se na korišćenju odgovorajaćih algoritama upravljanja energetskim pretvaračima, kojima se može obezbediti jedinični faktor snage i oblik stuje čiji je harmonijski sastav u propisanim granicama. Pri malom udelu u mreži, negativan uticaj primene energetskih pretvarača je zanemarljiv. Međutim, pri povećanju prisustva ovih uređaja sa standardnim upravljanjem, situacija u elektroenergetskom sistemu se menja u pogledu promenljivosti inercije i učestanosti, što nije bila karakteristika tradicionalnih sistema. U ovim sistemima su se u elektranama koristili sinhroni generatori sa nepromenljivom inercijom rotora i prigušnim namotajem. U skladu s tim, veliki broj novonastalih problema bi se mogao prevazići povećanjem inercije i prigušenja u prelaznim procesima u elektroenergetskoj mreži. Jedan od načina za implementaciju navedenih svojstava sinhrone mašine u decentralizovanom sistemu jeste primena novog koncepta upravljanja, upravljanje energetskim pretvaračem kao virtuelnom sinhronom mašinom, koje se zasniva na matematičkom modelu sinhrone mašine. Na taj način energetski pretvarači, iako zapravo statički uređaji, dobijaju osobine obrtne mašine. Za razliku od pretvarača kod kojih je implementirana regulacija struje i koji predstavlaju stujni generator, virtuelna sinhrona mašina, poput klasične mašine, predstavlja naponski izvor. U radu je razmatran aktivni ispravljač upravljan kao virtuelna sinhrona mašina. Ovim načinom upravljanja održava se napon na jednosmernoj strani na zadatoj vrednosti i vrši se regulacija reaktivne snage, čime se može obezbediti jedinični faktor snage. Prikazano je modelovanje sinhrone mašine, kao i aktivnog ispavljača sa emuliranom inercijom i prigušnim namotajem. Dato je poređenje rezultata simulacija na razvijenim modelima u oba slučaja i izvedeni su odgovarajući zaključci na osnovu sprovedene analize. Ključne reči: aktivni ispravljač, virtuelna sinhrona mašina, sinhroni generator, energetska efikasnost, obnovljivi izvori energije Due to growing requirements for renewable energy sources integration into power system with the aim of its decentralization, the use of power converters is constantly increasing. There is also a greater number of applications in industry with controlled electrical drives that include power converters owing to realization of complex production processes demands. Consequently, there are new emerging problems with power grid regarding stability, voltage quality, current distortion and energy efficiency. To eliminate some of mentioned drawbacks, different power converters control algorithms exists, which can provide unity power operation and sinusoidal grid currents with harmonics content according to standards. The negative impact of the power converters use is negligible with their small share in the power grid. But, the growing presence of these devices with typical control techniques lead to changed situation in power systems considering variable inertia and frequency, what was not the traditional system characteristic. Power plants in those systems implied synchronous generators with constant rotor inertia and with a damper winding. Consequently, a great number of emerging problems could be overcome by increasing inertia and damping in transient processes in the power grid. One of the approaches to implement the mentioned properties of a synchronous machine in a decentralized system is the application of a new control concept, the control of the power converter as a virtual synchronous machine, which is based on the mathematical model of the synchronous machine. In this way, power converters, although actually static devices, acquire the characteristics of a rotating machine. Unlike power converters with current controllers which act as current generators, a virtual synchronous machine, like a classical machine, acts as a voltage source. The paper analysis active rectifier controlled as virtual synchronous machine. With this control method, the voltage on the DC side is maintained at the constant value and the reactive power is controlled, thus providing a unit power factor operation of the power control. Synchronous machine modeling, as well as modeling of active rectifier with emulated inertia and damper winding is presented in the paper. Comparative study of results of simulations on developed dynamical models in both cases is conducted, with the derived conclusions. Key words: active rectifier, virtual synchronous machine, synchronous generator, energy efficiency, renewable energy sources

Kvalitet električne energije predstavlja jednu od značajnijih oblasti u elektro-energetici, koja je postala naročito aktuelna sa naglim porastom zastupljenosti energetskih pretvarača u industriji i domaćinstvima. Ovi uređaji predstavljaju nelinearne potrošače koji unose neželjeni sadržaj viših harmonika u sastav mrežne struje i napona. Aktivni ispravljač, kao energetski pretvarač, u sebi sadrži tranzistore koji svojim komutacijama dovode do negativnih efekata u harmonijskom sastavu mrežne struje, a koji postaju još izraženiji ukoliko se ispravljač napaja mrežnim naponom koji nije prostoperiodičan.Visok sadržaj harmonika u linijskoj struji stvara niz problema u distributivnim sistemima, poput: • izobličenja napona i elektromagnetne interferencije (EMI), koji utiču na druge uređaje u distributivnom sistemu; • smanjene vrednosti faktora snage potrošača; • otežanog rada upravljačkih kola drugih elektronskih uređaja u distributivnom sistemu. Za razliku od diodnih i tiristorskih, kod aktivnih ispravljača se komutacije dešavaju sa daleko većim vrednostima učestanosti, što im i daje glavnu prednost u odnosu na mrežom vođene ispravljače. Prednosti koje takva topologija pruža su: • rad sa ukupnim (pravim) faktorom snage vrlo bliskim jedinici; • mogućnost vraćanja celokupne regenerisane energije u mrežu; • sinusoidalni talasni oblik ulazne (mrežne) struje i u motornom i u generatorskom (regenerativnom) režimu rada. Kao obavezan sastavni deo konfiguracije sa aktivnim ispravljačem koristi se energetski LCL filtar za eleminaciju harmonika na učestanostima komutacije i njenih celobrojnih umnožaka. On predstavlja bitan element u pogledu očuvanju kvaliteta mrežne struje, zbog čega je u radu prikazan detaljan postupak za njegovo pravilno projektovanje. Svaka distorzija mrežnog napona, čak i u granicama dozvoljene, negativno utiče na harmonijski sadržaj linijskih struja. U ovom radu je modelovan aktivni ispravljač koji se napaja naponom iz realnog izvora, a koji u sebi sadrži više harmonike u standardom definisanim granicama, sa ciljem da se primenom energetskih filtara i digitalne obrade signala postigne da ulazna struja u ispravljač bude što približnija sinusoidi. Rezultati simulacija na modelu aktivnog ispravljača sa primenjenim LCL filtrom, za koji je detaljno prikazana metoda izbora parametara sa jasnim opisom kriterijuma za njihov izbor, potvrdili su očekivano smanjenje harmonijskog sadržaja struje sa mrežne i ispravljačke strane.

Sinhroni motori sa stalnim magnetima (PMSM) imaju sve češću primenu u regulisanim elektromotonim pogonima, pre svega zbog veće energetske efikasnosti u odnosu na druge motore. Imaju veliku gustinu snage, dobar prenos toplote i povoljne upravljačke karakteristike, zbog čega se pored ostalih aplikacije koriste i u servopogonima. Razlikuju se prema načinu ugradnje stalnih magneta u magnetsko kolo rotora. Način ugradnje znatno utiče na parametre motora. Sinhroni motori sa stalnim magnetima utisnutim u rotor (IPMSM) pripada grupi motora sa unutrašnjom montažom stalnih magneta i ove motore karakterišu različite vrednosti induktivnosti po uzdužnoj i poprečnoj osi. Princip projektovanja ovog tipa motora ukratko je objašnjen u prvom delu rada. Pri projektovanju su korišćene analitičke relacije za proračun dimenzija i parametara motora, a zatim je vršena verifikacija dobijene geometrije pomoću odgovarajućih softverskih alata. Najzastupljeniji način upravljanja pogonom sa sinhronim motorom sa stalnim magnetima je vektorsko upravljanje. Primenom dodatnih strategije upravljanja koje se zasnivaju na vektorskom upravljanju mogu se ostvariti zahtevane performanse pogona. U radu su analizirane četiri strategije upravljanja pogonom sa sinhronim motorom sa stalnim magnetima i to: - upravljanje pri konstantnom uglu momenta; - upravljanje pri jediničnom faktoru snage; - upravljanje pri konstantnoj vrednosti fluksa u zazoru mašine; - upravljanje pri optimalnom odnosu momenta i struje. Ova četiri načina upravljanja su implementirana na detaljno razvijenom modelu pogona koristeći parametre prethodno projektovanog sinhronog motora. Predstavljeni su rezultati simulacija, na osnovu kojih je izvršena uporedna analiza razmatranih strategija upravljanja u cilju postizanja boljih performansi pogona. Izveden je zaključak o uticaju parametara ovog tipa motora na radne karakteristike pogona, kao i na mogućnost rada pogona u režimu slabljenja polja.

Energetska efikasnost je poslednjih godina dobila na značaju, posebno kada je došlo do značajnih promena na tržištu energijom i energentima. Kada se uporede vrednosti iz 2008. i 2022., cena električne energije se gotovo udvostručila (podaci EuroStat-a). Tokom poslednjih nekoliko decenija sve je aktuelnija proizvodnja „čiste“ električne energije iz obnovljivih izvora energije-OIE, međutim potpun prelazak na proizvodnju električne energije iz OIE nije izvestan u bliskoj budućnosti. U radu je analizirana mogućnost za povećanje energetske efikasnosti na primeru jednog industrijskog postrojenja gde je sproveden kratak energetski pregled. Predložene su mere za unapređenje energetske efikasnosnosti i urađena je jednostavna analiza njihove finansijske isplativost. Mere za unapređenje energetske efikasnosti koje su prkazane u ovom radu se, pre svega, odnose na smanjenje harmonijskog sastava u talasnim oblicima napona i struje, čime se smanjuju gubici kako u prenosu električne energije, tako i u njenoj eksploataciji. Velika pažnja u radu je posvećena i kompenzaciji reaktivne energije, koja predstavlja veoma važan faktor u povećanju energetske efikasnosti. Dodatno, u radu je analizirana mogućnost izgradnje solarne elektrane sa ciljem povećenja energetske efikasnosti celokupnog postrojenja. Izabrani su solarni paneli, način i mesto za njihovo postavljanje, dimenzionisan je invertor i izračunata je potencijalna proizvodnja električne energije. Takođe je detaljno analizirano rukovanje „viškom“ proizvedene energije u skladu sa poznatim paramtrima postrojenja (mogućnost korišćenja baterija za skladištenje energije). Energy Audit in Selected Industrial Company and Proposed Measures for Energy Efficiency Improvements The paper presents the main results of an energy audit in a selected industrial company. Particular focus was on the analysis of data on energy consumption and calculation of KPI regarding the EE. In addition, we analyzed the possibility of installing a PV solar power plant with or without batteries. According to the measured data, the evaluation of condensation battery reparation and replacement was included in this paper. The list of possible measures for improvement of energy efficiency is also presented.

Velocimetry has a long tradition in Serbia. Anyhow, constant improvement of the laboratories calibration and measurement capabilities (CMC) is an ongoing effort. Serbia, although it has good capabilities in this field, still doesn’t have a national standard for velocimetry. Reliable velocimetry is a starting point in various sectors of energy production, numerous industrial branches, health, educational, business and sport centers, as well as in residential buildings, and etc. Realization of this national standard would influence and improve national industry capabilities, energy efficiency in general, health and environmental protection procedures, climate analysis, forecasts and hydrology. Various international and national standards treat velocimetry, especially, as a tool in determination of the flow rate in closed conduits and open channels. This opens a whole new area of validation of the volume flow rate calibration in laboratory, as well as in situ. In this paper will be presented novel velocimetry techniques and their capabilities implemented in the Laboratory for turbulence and velocimetry at the Faculty of Mechanical Engineering. Here are presented following measurement techniques: multihole probes, hot-wire anemometry, laser Doppler velocimetry (three-component) and image-based velocimetry techniques (particle image velocimetry (PIV) and micro PIV). In the Laboratory are implemented stereo PIV and high speed stereo PIV. In addition to this, constant upgrading of the existing systems is followed by the development of the new techniques and procedures. These complex measurement techniques are employed in research of various flow phenomena, what will be presented in short.

Abstract Ball valves are one of the most commonly used valves in a wide variety of industrial applications. In this paper it is presented how the characteristics of the ball valve Giacomini R850 were experimentally and numerically determined. The experiment is carried out by simultaneously measuring the pressure drop between the measuring sections and the volume flow rate. The experiment is performed for 7 valves positions, i.e. for 7 different values of the valve angle in the range from 5º to 50º. After the experimental investigation, numerical simulations of water flow through the ball valve are performed. Numerical calculations are done by using OpenFOAM software. The Reynolds statistical approach (RANS) is used for treating turbulence. The turbulent viscosity is modeled by the standard k-ɛ turbulent model, and the SIMPLE algorithm is used as a numerical procedure for solution of RANS equations. In the numerical simulations, three different valve angles are analyzed (5º, 10º and 15º). For each position of valve, there are 6 cases with different volume flow rates in the range from 0.6 to 1.3 lit/s that are examined. Finally, experimental and numerical results are compared for three valve positions. It is concluded that the performed numerical simulations successfully predict the pressure drop on the valve, i.e. they successfully determine the characteristics of the considered ball valve. Keywords: Ball valve, turbulence, CFD, OpenFOAM Апстракт Кугласти вентили су међу најчешће коришћеним вентилима у различитим индустријским постројењима. У овом раду приказано је како се експериментално и нумерички одређује карактеристика кугластог вентила Giacomini R850. Експеримент је извршен истовременим мерењем пада притиска између мерних пресека и запреминског протока. Експеримент је извршен за 7 позиција вентила, тј. за 7 различитих вредности угла закретања вентила у опсегу од 5º до 50º. Након експерименталног испитивања извршене су нумеричке симулације струјања воде кроз кугласти вентил. Симулације су извршене коришћењем софтвера OpenFOAM. За третирање проблема турбуленције коришћен је Рејнолдсов статистички приступ. Турбулентна вискозност моделирана је стандардним k-ɛ турбулентним моделом, а SIMPLE алгоритам је коришћен за решавање Рејнолдсових једначина. Нумеричке симулације су извршене за три положаја вентила (5º, 10º and 15º). За сваки положај вентила разматрано је 6 случајева са различитим вредностима запреминског протока у опсегу од 0.6 до 1.3 lit/s. На крају, извршено је поређење експерименталних и нумеричких резултата за три положаја вентила. Закључено је да извршене нумеричке симулације успешно предвиђају пад притиска на вентилу, тј. успешно одређују карактеристике разматраног вентила. Кључне речи: Кугласти вентили, турбуленција, CFD, OpenFOAM

Control valves have numerous applications like in natural gas control and transport (as anti surge and recycle valves, hot/cold bypass valves, throttling valves, degasser flow/level control valves), natural gas treatment for dehydration and desulphuring (TEG injection, flashing drum pressure control, amine pump recirculation control valves), LNG processing (gas/steam to vent valves, blowdown and depressing valves), refineries and petrochemical (charge pump recycle valves, blowdown control valves, emergency vent valves, amine pump recycle valves), ethylene plants (feed-pump recycle valve, blowdown and gas to vent/flare valves, steam conditioning and desuperheating, compressor recycle) and etc. Valve trim is consisted of cage or dick stack, plug, stem and seat. Size from app. 15.88 mm (0.625 in) up to 101.6 mm (4 in) is suitable for 3D metal print, what is presented in this paper. Selective laser melting 3D metal printing is applied on the disc presented in this paper. Even better material properties from rest of the valve parts could be obtained. This is of great importance for valve retrofitting. In this paper is presented, also new developed channel geometry, what is followed by various fluid flow phenomena. Here is shown, in short, procedure for determination of KV-Values of the test valves according to the EN 60534-2-3, Industrial-process control valves - Part 2-3: Flow capacity - Test procedures. Some aspects of CFD calculations will be presented, also.

Cilj ovog rada je da prikaže primere iz prakse nekih od složenijih problema u vodovodnim sistemima, kao i načine neinvazivnog otklanjanja istih, na što slikovitiji način, korišćenjem rešenja iz proizvodnog programa ARMAS, a u nadi da će biti od pomoći svima u otklanjanju istih ili sličnih problema kada se sa njima susretnu. Rad je prevashodno baziran na raznim problemima koji nastaju usled procurivanja cevi, kao i usled pucanja cevi na dužinama manjim od 1m, budući da se za pucanja na većim dužinama od navedene mora zameniti oštećeni deo cevovoda novim. Iako se u održavanju i rekonstrukciji cevovodnih sistema gotovo svaki problem može iskomplikovati i pokazati jako složenim, cilj ovog rada je da prikaže neke od primera za koje nije bilo rešenja u postojećoj ponudi proizvoda na tržištu i za koje je ARMAS izradio nove i inovativne proizvode kako bi problemi bili brzo i uspešno otklonjeni, uz osnovni cilj da ne dođe do isključivanja potrošača i sečenja cevi.

Одводњавање муља, односно редукција његове запремине смањењем удела воде представља један од најбитнијих процеса у преради отпадне воде. Циљ је да се удео воде смањи уз минималну потрошњу енергије и минималне трошкове одржавања опреме. Током два месеца тестирана је вијчана преса на једанаест локација и извршено је поређење различитих технологија одводњавања муља. Мерење процента суве материје је вршено и пре и након тестирања опреме. Вијчана преса се показала као најбоље решење у свим случајевима.

The study aimed to show in a systematic way possible energy efficiency measures that would decrease the total energy use at the university campus in Trondheim, Norway. The entire study was developed in close collaboration with the NTNU Property and Technical Management divisions, meaning that suggested energy efficiency scenarios and other assumptions were highly relevant. The study was a part of feasibility study for campus development. Currently, the campus floor area is about 300 000 m2 and consists of buildings combining offices, lecturing halls, study halls, and laboratories. The campus building stock has been built from 1910 to 2002. To perform this study, building performance simulation and material flow analysis method were combined. Reference building models for each university cohort were developed based on the methodology for defining the reference buildings. The material flow analysis model was utilized to aggregate the outputs from the building simulation and evaluate global effects of energy efficiency measures. The results of the single reference building analyses showed that a decrease of up to 50% in heating energy use might be achieved by increasing efficiency of the ventilation system and by decreasing the temperature of the heating system. The results showed that in spite of building stock growth, the estimated energy use would decrease from 2017 to 2050 by 10% for the standard renovation rate, and by 26% for the combination of ambitious renovation and technical improvements.

A single data centre may consume as much electricity as a small city. Most of this electricity use will be converted into waste heat that is emitted into the environment. Recent studies have found that there is tremendous potential for using data centre waste heat for district heating (DH). Meanwhile, pilot projects being conducted around Europe have demonstrated the technical and financial feasibility of this concept. However, using data centre waste heat for DH systems still has a lot of space for improvement. Firstly, temporal mismatches between the data centre waste heat supply and DH heat demand usually exist. These mismatches result in surplus waste heat, which still needs to be emitted into the environment. Secondly, DH systems usually use fossil fuels to cover peak heat demand, meaning higher operating costs and more emissions at peak hours. To achieve better economic and environmental performance, the non-dispatchable waste heat supply should be shifted for peak load shaving. This article aimed to solve these problems by introducing thermal energy storage (TES). Three TES solutions were proposed, including a short-term water tank TES, a seasonal borehole TES, and both the short-term water tank and seasonal borehole TES, respectively. Detailed Modelica models were developed for these TES scenarios and a reference scenario before introducing any TES. The proposed method was tested on a campus DH system in Norway. Results showed that the water tank could shave the peak load by 31% and save the annual energy cost by 5%. The payback period was lower than 15 years when the storage efficiency remained higher than 80%. However, it had no obvious benefits in terms of mismatch relief. In contrast, the borehole TES increased the waste heat utilization rate to 96%. However, the payback period was more than 17 years.

The combined production of electricity and thermal energy (CHP or cogeneration) is the most efficient and convenient approach to reduce costs for energy at industrial power plants and district heating plants that use natural gas as fuel in order to produce thermal energy for various needs. In this paper the operational characteristics of the CHP plant, which has been operating since January 1, 2021 at the Voždovac Heating Plant as part of the Belgrade district heating system are analyzed. The CHP plant consists of three gas engine unites with a total nominal electric power of 10 MW and a thermal power of 10.1 MW, which use natural gas as fuel. The CHP plant is used for district heating purposes and the preparation of domestic hot water (DHW) while electricity is sold to the local electric grid. The emphasis of the analysis in this paper is on the operational characteristics of the plant: the number of working hours, the total energy consumption and energy production, the efficiency as well as the operational and maintenance costs. Also, the impact of the drastic changes in the prices of natural gas, electricity and maintenance costs in the last year on the financial profitability of the CHP plant was analyzed in particular.

Program Ujedinjenih nacija za razvoj (UNDP), u partnerstvu sa Ministarstvom rudarstva i energetike (MRE) Republike Srbije (RS) i Razvojnom bankom Saveta Evrope (CEV) i u neposrednoj saradnji sa Upravom za zajedničke poslove republičkih organa (UZZPRO) sprovodi projekat predviđen za pripremne aktivnosti za sprovođenje programa: „Energetska efikasnost u zgradama centralne vlasti“. Ovaj višegodišnji program ima za cilj energetsku sanaciju zgrada centralne vlasti (ZCV) u skladu sa članom 5 Direktive o energetskoj efikasnosti (2012/27 / EU) (EED). Program obuhvata energetsku sanaciju do 28 ZCV u Beogradu ukupne površine 208.000 m2, od čega su 50% zgrade pod zaštitom. Program bi za rezultat trebalo da ima najmanje 30% smanjenja potrošnje primarne energije, oko 20% smanjenja CO2, poboljšanje uslova rada, poboljšanje bezbednosti na radu i oko 29% uštede u operativnim troškovima za energiju. Pored toga, program treba da doprinese zaštiti i očuvanju zgrada kulturne baštine. Vlada RS je sa SEV ugovorila zajam od 40 miliona EUR za energetsku sanaciju pomenutih 28 ZCV koji je potpisan od strane ministra finansija RS u martu 2020. godine i ratifikovan od strane Skupštine RS u novembru 2020. godine. Predviđeno je da Program sprovedu MRE i UNDP, u saradnji sa UZZPRO tokom perioda od 5 godina. Pripremne aktivnosti koje su u toku finansiraju donatori Povereničkog fonda CEB (Slovačka i Španija) i EU Investicioni okvir za Zapadni Balkan (WBIF). Glavne pripremne aktivnosti predviđene projektom su: obezbeđivanje tehničkih usluga, izrada energetskih sertifikata za postojeće stanje (u skladu postojećim propisima), izrada detaljnih energetskih pregleda (DEP) zgrada, izvođenje geoloških istraživanja radi procene geotermalnog potencijala na lokacijama zgrada „Palata Srbija“ i SIV 3, izrada studija izvodljivosti energetske sanacije za zgrade „Palata Srbija“ i SIV 3 i izrada projektne dokumentacije različitog nivoa složenosti, a na osnovu rezultata DEP-a.

The Peltier or thermoelectric effect has been known for more than a century, but it has found adequate commercial application only in recent decades. Of course, one of the reasons is the price, because the use of low-efficiency thermoelectric modules can only be justified by the low price of the product. The aim of this paper is an experimental analysis of the possibility of using thermoelectric modules for heating a building using renewable energy sources. It is not necessary that the energy generator for the thermoelectric module is solar energy, but the concept of the system is to work without freon and without negative and harmful effects on the environment. The preparation of energy from renewable energy sources that will be used in freon refrigeration devices is lacking precisely because of the working means that must be reduced by 2030. Solar heating is not justified without solar cooling, due to the fact that there are adequate solutions for solar heating and preparation of hot water, but it is studied here to combine as a complete solution of thermal comfort in the room together with cooling. The experiment was designed so that the Peltier element was positioned on the heat exchangers and the measurement of the input current and all temperatures was performed. The heat exchanger, as well as the space that simulates the living room of a residential building, is scaled by dimensional analysis due to the cost of installation. Measurements are made primarily for the element itself and then with heat exchangers on both sides of the element. A detailed mathematical model of heat transfer was made in order to analyze the dimension of the heat exchanger, while a more detailed analysis of the shape of the heat exchanger and optimization of the number of modules are planned in the future. The system is designed with a module built into the wall of the building, where it is necessary to measure indoor and outdoor air temperatures, surface temperatures of the Peltier module and heat exchangers at several points, as well as input voltage and input current that generate temperature difference on the module. The paper primarily defines the thermoelectric effect and the Peltier element throughout history, and then the justification for the use of this system for heating the building by analyzing previous research. Due to the comfort in the space, the heat exchange was analyzed by natural convection, that is, without additional fans.

U cilju obezbjeđivanja sigurnosti, pouzdanosti i dobrih performansi projektovanog sistema, neophodno je sprovoditi analize hidrauličkih prelaznih procesa izazvanih dvofaznim strujanjem zarobljenog vazduha i vode u cijevnim sistema pod pritiskom. Dvofazna strujanja sa interakcijom zarobljenog vazduha i vode javljaju se u industrijskim sistemima, kao što su hidroelektrane, pumpne stanice, distributivni vodovodni i kanalizacioni sistemi, itd. U hidrauličkim sistemima vazduh se uglavnom može nalaziti u vidu nepokretnih džepova ili pokretnih mjehurića, koji u zavisnosti od njihove veličine i lokacije, kao i, konfiguracije cjevnog sistema, mogu stvoriti ozbiljne smetnje u radu. Kompleksno kretanje vazdušnog džepa uslijed interakcije sa vodom, kao i nepredvidivo ponašanje dodirne površine (interfejsa) između ova dva fluida, čine ove hidrauličke procese veoma teškim i izazovnim za numeričko simuliranje, pa je za ozbiljnije analize primjena višefaznih modela obavezna. U ovom radu, primjenom računske dinamike fluida (CFD) sa modelom zapremine fluida (VOF), izvršiće se numeričko modeliranje, eksperimentalno istraživanje i simulacija prelaznih procesa izazvanih dvofaznim strujanjem vazduha i vode tokom brzog punjenja horizontalne cijevi za različite početne uslove, tj. različite veličine vazdušnih džepova, vrijednosti početnog pogonskog pritiska i dimenzija otvora na kraju posmatranog sistema. Cilj ovog istraživanja je sagledavanje fenomena koji se javljaju uslijed brzog punjenja cijevi, uključujući fizičko razumijevanje nagle promjene pritiska u cijevnim sistemima koji sadrže zarobljeni vazduh.

A representative assessment of the combustion plant's impact on air quality is the basis for making decisions both in the design phase of the plant itself or its parts and for defining spatial planning and strategic decisions. Given that dispersion models represent a mathematical expression of the synergy of atmospheric processes, relief and characteristics of emitters, the main problem in their use is the type, amount and accuracy of data that are required to obtain sufficiently reliable results through a specific model. The paper presents the basic principles of modeling as well as examples of results for different combustion plants. MODELOVANJE ATMOSFERSKE DISPERZIJE ZAGAĐUJUĆIH MATERIJA IZ TERMOENERGETSKIH POSTROJENJA Reprezentativna procena uticaja termoenergetskog postrojenja na kvalitet vazduha predstavlja osnov za donošenje odluka kako u fazi projektovanja samog postrojenja ili njegovih delova tako i za definisanje prostorno-planerskih i strateških odluka. Obzirom da disperzioni modeli predstavljaju matematički izraz sinergije atmosferskih procesa, reljefa i karakteristika emitera, osnovni problem kod njihovog korišćenja je vrsta, količina i tačnost podataka koji su potrebni da bi se putem određenog modela dobili dovoljno pouzdani rezultati. U radu su prikazani osnovni principi modelovanja kao i primeri rezultata za različita termoenergetska postrojenja.

Abstract: Hydrogen is a very important energy carrier which can make a decisive contribution to the future energy transition. It may be produced using several technologies, may be stored and transported in several ways. It may be used to cover different energy needs, like transportation, power and heat generation, iron ore reduction etc. Nowadays well over 90% of existing Hydrogen on the market is “grey”, i.e. obtained from primary fossil fuels with accompanying high CO2 emissions. If the carbon dioxide produced during the steam reforming of Methane is subsequently separated from the process and stored underground, such Hydrogen is referred to as “blue” hydrogen. Methane cracking is recently intensively developing: it is broken down at high temperatures (in the presence of some catalyst, or without it) into its molecular components. Storing or using of solid carbon is much easier and more attractive than storage of CO2. Hydrogen produced in this way is referred to as "turquoise". The process without catalysts is simpler, but requires higher temperatures. The test facility consists of two columns filled with pebble-bed and a connecting horizontal part. The upper part of the pebble-beds and the connecting pipe is the highest temperature zone where the cracking process mainly takes place. In the high temperature zone, the cracking process is very intensive and the required reaction energy is supplied by adding some oxygen to burn small amount of Hydrogen. Sensible heat of product gas is stored in the pebble-bed and cold gas goes out. In a condenser, the product gas is further cooled, and the occurred condensate flows in a drain vessel. After some time, by switching corresponding valves, the flow direction is changed, so that Methane enters the second pebble-bed and the product gas goes out through the first pebble-bed. The capacity of the test facility was 2 – 4 of Methane, with corresponding residence time in the range 0.5 to 2 seconds. At above 1450°C, the H2-ratio was always above 90%. In order to compare the quality of the achieved results, the yield of Hydrogen was evaluated for the best test results. The highest yields have been achieved at temperature above 1500°C, with a maximum value of 94.9% at 1560°C. Those results are considerably better than those achieved in other test facilities for cracking using catalysts (the highest yield 78% at 1175°C). That comparison shows important advantages of the high temperature process without catalyst. If one has the experience and technology for high temperatures (1500°C and more) that is a simpler and more effective way to reach industrialization of cracking technology. Apstrakt: Vodonik je veoma važan nosilac energije koji može dati odlučujući doprinos budućoj energetskoj tranziciji. Može se proizvoditi korišćenjem nekoliko tehnologija, a može se skladištiti i transportovati na više načina. Koristiti će se za pokrivanje različitih energetskih potreba, kao što su transport, proizvodnja električne energije i toplote, redukcije gvozdene rude itd. Danas je više od 90% postojećeg vodonika na tržištu „sivo“, tj. dobijeno iz primarnih fosilnih goriva sa pratećim visokim emisijama CO2. Ako se ugljen-dioksid nastao tokom parnog reformisanja metana naknadno odvoji i uskladišti pod zemljom, takav vodonik se naziva „plavi“ vodonik. Krekovanje metana se u poslednje vreme intenzivno razvija: on se na visokim temperaturama (u prisustvu nekog katalizatora ili bez njega) razlaže na svoje molekularne komponente. Čuvanje ili korišćenje čvrstog ugljenika je mnogo lakše i privlačnije od skladištenja CO2. Vodonik proizveden na ovaj način se naziva "tirkizni". Proces bez katalizatora je jednostavniji, ali zahteva više temperature. Ogledni objekat se sastoji od dve kolone (pebble-bed) ispunjene kugličnim zasipom i veznog horizontalnog dela. Gornji deo pebble-beda i spojna horizontalna cev je zona najviše temperature u kojoj se uglavnom odvija proces krekovanja. U toj zoni visoke temperature, proces je veoma intenzivan i potrebna reakciona energija se obezbeđuje dodavanjem kiseonika za sagorevanje male količine vodonika. Osetna toplota procesnog gasa se skladišti u kugličnom zasipu i hladni gas izlazi. U kondenzatoru se procesni gas dalje hladi, a nastali kondenzat se odvaja u drenažni sud. Nakon nekog vremena, prebacivanjem odgovarajućih ventila, smer protoka se menja, tako da metan ulazi u drugi pebble-bed, a procesni gas izlazi kroz prvi pebble-bed. Kapacitet opitnog postrojenja je bio 2 – 4 metana, sa vremenom zadržavanja u rasponu od 0,5 do 2 sekunde. Na temperaturi iznad 1450°C, udeo H2 je uvek bio iznad 90%. Da bi se uporedio kvalitet postignutih rezultata, prinos vodonika je izračunat za najbolje rezultate ispitivanja. Najveći prinosi su postignuti na temperaturi iznad 1500°C, sa maksimalnom vrednošću od 94,9% na 1560°C. Ovi rezultati su znatno bolji od rezultata postignutih u drugim postrojenjima za ispitivanje krekovanja pomoću katalizatora (najveći prinos 78% na 1175°C). To poređenje pokazuje važne prednosti procesa pri visokoj temperaturi bez katalizatora. Ako se poseduje iskustvo i tehnologija za visoke temperature (1500°C i više) to je jednostavniji, brži i efikasniji način da se dođe do industrijalizacije tehnologije krekovanja metana.

Hydrogen produced via the thermal decomposition of natural gas, also known as ‘turquoise’ hydrogen, is the subject of this study. It is expected that ‘turquoise’ hydrogen will play a significant role in the coming energy transition, reducing emissions from fossil fuels in the short term until renewable energy sources are capable of producing enough energy or hydrogen transport becomes feasible on a large scale. The main advantage of the thermal decomposition of natural gas is the possibility of obtaining a high yield of hydrogen without the emission of carbon monoxide or carbon dioxide since the main products of the process are carbon in a solid state and hydrogen. Using plasma in the process elevates the temperature of the process and increases methane decomposition without catalysts. This paper analyses the process using a thermodynamic equilibrium model based on the minimum of the Gibbs function in the temperature range of 500 - 2 000 K. As a result of the study, the equilibrium composition of the system in the observed temperature range is presented. Also, attention is given to undesirable components in the system such as carbon dioxide, hydrocyanic acid, and nitrogen compounds like ammonia and nitrogen monoxide. From the point of energy analysis, the useful energy of the system per kilogram of fuel and the efficiency of the process is presented. The results of the numerical analysis show that the efficiency of the process increases with increasing temperature and reaches its maximum at a temperature of 1200 K when an energy efficiency of about 50% is achieved.

Abstrakt Broj stanovnika u urbanim zonama se konstantno povećava što, u kombinaciji sa drugim faktorima, dovodi do pogoršanja kvaliteta vazduha. Jedan od najvažnijih parametara koji se meri u okviru monitoringa kvaliteta vazduha je koncentracija finih čestica (PM – particulate matter). One su povezane sa mnogim zdravstvenim problemima, na primer oboljenjima srca i pluća. U ovom radu predstavljamo prototip senzorskog sistema za praćenje koncentracije PM2.5 čestica, baziran na Arduino platformi. Sistem se sastoji od više senzora (senzor koncentracije PM2.5 čestica, senzor temperature i vlažnosti vazduha, senzor koncentracije ugljen-monoksida, itd), koji su povezani na Arduino Uno R3 pločicu sa Atmega328P mikrokontrolerom. Testiranje sistema je izvršeno u trajanju od deset uzastopnih dana, pri čemu su svakog dana merenja izvođena na šest lokacija. Pored senzora kvaliteta vazduha sistem je opremljen i GPS prijemnikom, te su dobijeni podaci bili georeferencirani. Oni su potom korišćeni za generisanje rasterskih mapa u GIS okruženju, kako bi se kvalitetnije vizuelno predstavila prostorna raspodela merenih parametara. Primenjeni pristup, iako sa određenim nedostacima, predstavlja dobru osnovu za GIS-bazirani sistem za permanentni monitoring kvaliteta vazduha. Abstract Population in urban areas is constantly increasing which, in combination with other factors, leads to degradation of air quality. One of the most important parameters that has to be measured in air quality monitoring is concentration of fine particles (PM – particulate matter). They are linked with various health hazards, such as heart and lung diseases. In this paper we are presenting a prototype of a sensor system for monitoring of PM2.5 particles, based on Arduino platform. The system consists of several sensors (PM2.5 concentration sensor, air temperature and humidity sensor, carbon-monoxide sensor, etc.), that are connected to Arduino Uno R3 evaluation board with ATmega328P microcontroller. The system was tested during ten consecutive days. Each day the measurements were performed on six location. Besides air quality sensors, the system is equipped with GPS sensor too, so collected data are georeferenced. They were used to create raster maps in GIS environment, in order to better visualize the spatial distribution of pollutants. Applied approach, although with some drawbacks, appeared to be a good basis for a GIS based system for permanent air-quality monitoring.

A concise one dimensional thermal-hydraulic two-fluid model is presented for the numerical prediction of sulphur dioxide absorption from the flue gas onto drops of the water-limestone slurry in the vertical spray tower absorber. The model is based on mass, momentum and energy balance equations for each phase separately, i.e. downward falling droplets of water-limestone slurry and upward flowing flue gas. The sulphur dioxide content in the flue gas is predicted by a balance equation of the sulphur dioxide mass fraction in the flue gas. Interface transfer processes between the flue gas and the droplets are determined by closure laws. The obtained steady-state balance equations are transformed in a form suitable for a direct application of the numerical integration method for the system of ordinary differential equations. The developed thermal-hydraulic model is validated by comparing numerical results with available measured data at the large utility absorber. The presented results clearly show the dynamics of flue gas and droplets thermal-hydraulic processes and their influence on the absorption process. The influence of liquid-to-gas ratio and droplet diameter on sulphur dioxide removal efficiency has been investigated.

In the paper, we analyze the operation of a plant producing refined alcohol with a capacity of 25,000 kg/day, which uses corn as the primary raw material. On the site location, there are a cow farm, a plant for the combined production of heat and electricity using biogas, and a distillery production plant. The raw material for biogas is manure from a cow farm. The energy required for the production process and the operation of the supporting systems (space heating, own consumption of the CHP plant, etc.) is obtained by burning biogas and ethanol so that fossil fuels are used only in cases of plant start-up or incident situations of production process failure. The analysis presented in this paper aims to set up a carbon dioxide balance for a production plant with accompanying systems and its comparison to the carbon dioxide consumption necessary for corn's growth.

Due to climate change urgency coal power plants are under immense pressure. A wave of closures is present all around the world. Especially in the EU the community that we aspire to join. CO2 tax is looming, and competitiveness with renewables is under decline. In this paper coal power plants are seen in future as a part of the energy storage system using excess electricity from renewables that would be otherwise curtailed. System consists of three parts: electricity to thermal energy conversion unit using heat pumps, electric heaters, or their combination, then energy storage system, and existing power plant running on Rankine cycle. Emissions would be zero, no SO2, no NOx, no CO2, no ultra-fine and very harmful particles. Jobs would be saved. Intermittence of renewables solved. Integration with industry and residential sector for heating and cooling is of great importance for the round-trip efficiency. Analysis is performed using Engineering Equation Solver.

Functional dependencies between the wind speed, RPM, current strength and voltage of wind turbines represent the basic indicator of their energy efficiency. In this sense, a series of tests of HAWT and VAWT were carried out in the Laboratory for Aerotechnics, the “Miroslav Nenadović” Wind Tunnel of the Faculty of Mechanical Engineering, University of Belgrade. In this paper, results of one such test are presented, where the observed functional dependencies showed the justification of using wind turbines as a source of electrical energy. The work is focused on a VAWT with non-standard type airfoil blades of different dimensions and poor finishing of the same. The dimensions of the wind turbine are adapted to the dimensions of the working part of the wind tunnel with an integrated constant consumer of electrical energy and a digital acquisition chain. The results of the wind turbine test from the unloaded state to the maximum load point to the optimal exploitation trend in terms of the efficiency of the wind turbine.

Different sources of renewable energy are available around us. One of the most suitable and clean renewable energy source is the wind. Vertical-axis wind turbines are insensitive to wind direction variations, that makes this type of wind turbines suitable for installations in urban areas. In the present work, noise levels, for 3 bladed vertical axis turbine (H-Darrieus type) were analyzed for different angles of attack. Turbine blade analyzed was symmetric airfoil (NACA series). Calculations were performed on a 2D model for 10 - 15 m/s inlet velocities. Pressure and velocity fields with noise broadband levels were calculated using RANS method for turbulence modeling. It was found that this approach can reveal the noise sources for this type of turbine in its operational regime. Furthermore, this method can be used in initial stages of turbine design, especially for airfoil selection for noise levels minimization.

Imajući u vidu da je energija neizostavan faktor koji utiče na dalji razvitak država u svetu, izvlači se logičan zaključak da se prema istoj treba odnositi sa većom pažnjom i posvećenošću nego danas. Smanjenje potrošnje ukupne energije čiji većinski udeo i dalje dolazi iz upotrebe fosilnih goriva, primenom mera energetske efikasnosti ili upotrebnom obnovljivih izvora energije poput solarne ili energije vetra, jedan je od načina na koji se prethodno pomenuti razvitak može podstaći. Poslednjih decenija zapažen je trend pogoršanja kvaliteta sirove nafte kao sirovine za preradu ali i uzlazni trend koji se tiče tehnoloških napredaka u oblasti prerade nafte i gasa sa ciljem proizvodnje čistijih i kvalitetnijih naftnih derivata. Takođe, poboljšanja imaju za svrhu i povećanje efikasnosti rafinerijskih procesa u smislu optimizacije prinosa, kvaliteta i svojstava produkata obrade i prerade nafte sa istovremenim smanjenjem na minimum količine otpadnih materija i materija koje ne mogu biti obrađene. Sa druge strane, činjenica je da su petrohemijska postrojenja sve starija, imajući u vidu da su velike rafinerije najvećih svetskih naftnih kompanija izgrađene sredinom ili u drugoj polovini prošlog veka, stvara se prilično plodno tlo za šarolike uzroke otkaza opreme. Životni vek opreme, koja je za potrebe petrohemijske industrije uglavnom jedinstvena i samim tim veoma skupa za izradu i održavanje, primenom metoda ispitivanja moguće je donekle produžiti u smislu dobijanja potvrde da je oprema dovoljno sigurna za rad i da ispunjava zadate radne parametre. Metodologija kojom je moguće uraditi gore navedeno je RBI (engl. Risk-Based Inspection, Ispitivanje zasnovano na riziku), čiji se doprinos najviše ogleda u povećanju bezbednosti rada samog postrojenja ali i u dodatnom smanjenju troškova prilikom održavanja. RBI pruža jedan sveobuhvatan inspekcijski plan koji utvrđuje termine ispitivanja a sve prema jedinstvenim karakteristikama postrojenja i procesnih parametara. Korak dalje u primeni klasične danas dobro ustanovljene RBI metodologije koja je razvijana i primenjivana poslednjih 20 godina jeste primena pristupa koji uzimaju u obzir dinamički aspekt rizika, poput dinamičke procene rizika ili proceni rizika koja je zasnovana na praćenju stanja opreme.

Aspen Plus has become one of the most widely used process modeling and simulation tools, which finds application in both academia and industry. Studies conducted using the Aspen Plus simulator have been widely applied to various technologies and feedstock. This paper aims to summarize advances and emphasize the significance of Aspen Plus in designing thermodynamic equilibrium models for the plasma gasification process and its application. We will present the characteristics of the thermal plasma gasification process, and modeling approaches, introduce thermodynamic equilibrium system modeling in Aspen Plus simulator, and highlight a review of developed models from the literature, emphasizing non-stoichiometric equilibrium models. The literature review points out the novelties in the recent developed models, as well as the influence of the most important operating parameters, such as temperature, equivalence ratio, selection of the gasifying medium, plasma power, and steam-to-feedstock ratio on the performance of the gasification process.

The field of renewable and sustainable energy is one of the most important topic in contemporary research, and various technologies related to energy saving are constantly reported. Solar energy is renewable, clean and practically nondepletable energy source - it is estimated that we will have steady, unlimited supply of sunlight for another 5 billion years. Efficient utilization of solar energy and development of solar systems in that purpose are the research topics of many scientists and engineers worldwide. Currently, there are two main kinds of such systems. The first is related to solar thermal power generation technologies where solar radiation is converted into heat, followed by particular power generation process in which thermal energy is converted to electrical energy. Technologies developed in that purpose are solar central power tower, parabolic trough solar thermal system and dish solar thermal technology. The second kind of solar systems are the ones in which solar energy is directly converted to electrical energy, where we can have light induction, photochemical or biological power generation. From the industry viewpoint, the usage of these systems as an alternate energy resource needs to meet reliability, performance and economic characteristics that compare favorably to conventional energy systems which can cover high energy demands. Unfortunately, the costs of developing large-scale power plants in MW scale for each of the aforementioned solar technologies are not feasible. The solar chimney power plant (SCPP) system, known also as solar updraft tower (SUT) uses solar energy to drive the air flow through turbines where kinetic energy of the air is converted into electric energy. This solar system has three essential parts: chimney, collector and turbines. The main role of collector is to absorb solar radiation and to heat up the air inside. Heated air has lower density than surrounding air in the environment, and due to buoyancy effect that environmental air pushes the heated air towards the center of the collector where high chimney is located. The role of the chimney is to create cumulative buoyancy and large pressure difference between the system and the environment, which causes the rise of the heated air from the collector into the chimney with great speed. Flowing air produces aerodynamic forces on the blades of axis-based turbine which cause the spinning of the rotor. This can be further converted to electrical energy via generator, with appropriate gear boxes. Turbine is usually installed at the bottom of the chimney, or several turbines can be placed near the collector outlet. In this paper, comprehensive review of the current research in area of SCPP will be presented, together with results of joint research previously presented in relevant literature, and their further elaboration. Additionally, new results from CFD simulations will be also presented. Main aspect of the research is focused on the analysis of the fluid flow and its effect on heat transfer in solar chimney power plant. Developed mathematical model and results of CFD simulations are validated using available experimental results from the prototype of SCPP which was build in Manzanares, Spain. Very good agreement with experimental results is obtained in both cases. Additionally, analysis of dimensionless form of model equations have shown that global efficiency can be improved with increase of global geometrical parameters of the plant, but on the other hand it is found that there is a limit value in relation between chimney height and mass flow rate through the system. Increase in chimney height increases the mass flow rate, but only to some extent.

A key role in energy management policies is played by the primary resource availability accommodation to the consumption. In such energy system, renewable energy resources play an important role. As these resources are variable in time, their forecast represents a significant issue. More and more attention is being paid to predicting a possible amount of electricity obtained on the basis of solar radiation on photovoltaic panels, which is influenced by numerous external parameters such as air temperature, amount of clouds and humidity. Numerous previous studies have shown that certain significant techniques which have been used to predict and optimize the performance of various solar energy systems are machine learning and artificial neural networks. Artificial neural networks (ANNs) are widely accepted as a technology that offers a solution to very complex problems, they can handle incomplete data and can perform high-speed prediction. ANNs process can be considered as a black-box modelling with a set of input factors and output variables which are results of input factors treatment through a systematic neural network. Back-propagation network is a type of multilayer feedforward neural network which achieves an arbitrary nonlinear map from inputs to outputs. In this research the back-propagation learning algorithm is used to construct a prediction model of photovoltaic power generation which can forecast the power outputs of photovoltaic system

Drvna sečka se sve češće koristi kao čvrsto gorivo u modernim kotlovima na biomasu. U Srbiji je u poslednjih dve do tri godine izgrađeno nekoliko postrojenja za sagorevanje biomase – drvne sečke sa ciljem da zamene brojna mala ložišta na ugalj niskog kvaliteta, kombinujući ih u jedno postrojenje. U predavanju će biti dat pregled konstrukcija i princip rada savremenih kotlova na drvnu sečku, kao i rezultati prijemnih ispitivanja kotlovskih postrojenja. Takođe, daće se osvrt na vrednosti emisija zagađujućih komponenata u vazduh iz navedenih postrojenja. Modern wood chips combustion plants – design, acceptance tests and emission of pollutants Wood chips are increasingly used as solid fuel in modern biomass boilers. In the last two to three years, several plants for burning biomass - wood chips have been built in Serbia with the aim of replacing numerous small low-rank coals burning plants, combining them into one plant. The lecture will provide an overview of constructions and the principle of operation of modern wood chip boilers, as well as the results of acceptance tests of boiler plants. Also, a review will be given of the emission values of polluting components into the air from the mentioned facilities.

Response Surface Method (RSM) is used to develop a mathematical model for modeling output parameters of a cooling tower. A series of experiments were performed on the experimental line, representing the industrial cooling tower model, to obtain the data needed to generate the model. Experiments are performed following the data matrix which enables that, by performing a minimum number of experimental runs, a mathematical model is generated. The inlet water temperature, water volume flow rate and air volume flow rate are configured as relevant input parameters (factors), while the output parameter is the water temperature at the outlet. Due to the limitations in the experimental setting, inlet air temperature and humidity are not varied during the experiments. Therefore, their influence on outlet water temperature is not considered. Using the experimental data, a quadratic polynomial regression model of outlet water temperature is generated, with selected inlet parameters as model factors. Model accuracy and adequacy are tested, showing excellent results. The analysis enables determining the input parameters that have the most significant influence on the output water temperature. It was concluded that the outlet water temperature is most affected by the inlet water temperature and air volume flow rate. The presented methodology can be applied to an industrial cooling tower in a thermal power plant or any other facility with a cooling tower included in the facility layout. Also, the generated model can be used for process optimization.

Ревитализација великих хидроелектрана углавном подразумева унапређење радних параметара великих хидроагрегата, док се за кућне мале хидроагрегате, који се користе за сопствену потрошњу, обично усвајају готова постојећа типска решења. Таква типизација ускраћује могућност разматрања више варијантних решења, која узимају у обзир фина побољшања енергетских параметара. У циљу целокупног унапређења енергетске ефикасности једне хидроелектране, размотрена је могућност побољшања енергетских карактеристика Пелтон турбине кућног агрегата који је у вишедеценијској експлотацији, задржавајући при томе постојеће улазне вредности протока и нето пада. Применом савремених препорука, урађена је упоредна анализа више варијантних решења модернизације кроз вишепараметарску анализу и пројектовање новог обртног кола. У раду су детаљније приказана изабрана решења којима је могуће остварити повећање номиналне снаге турбине и до 3,5% у односу на номиналну снагу постојеће турбине. Revitalization of large hydropower plants mainly implies enhancing the operating parameters of large hydro aggregates, while typical technical solutions are usually adopted for the small units auxiliary power supply. Such an approach can prevent the various solutions considering the refinement of the turbine energy parameters. In order to enhance the energy efficiency of the whole hydropower plant, a possibility to improve energy characteristics of a Pelton turbine for the station service power, which has been in exploitation for decades, is considered while retaining the existing input values of discharge and head. According to the contemporary recommendations, a comparative analysis of several variant technical solutions for modernization is carried out by multiparametric analysis with the design of a new turbine runner. In this paper, the chosen solutions are thoroughly presented, enabling an increase in the nominal power output of the improved turbine up to 3.5% in comparison to the existing one.

U periodu energetske tranzicije zemlje se suočavaju sa izazovima prelaska sa fosilnih goriva na OIE, što kao posledicu ima promjenu strukture energetskih proizvodnih kapaciteta, ali i potrebe postizanja održivog optimalnog energetskog miksa. Glavni cilj optimizacije energetskog miksa bio je izbor najefikasnije metode proizvodnje električne i toplotne energije unutar određenog nacionalnog/lokalnog područja. Višekriterijumska optimizacija je logičan način da se u potpunosti stvori realna slika trenutno optimalnog energetskog miksa, uzimajući u obzir neophodan i dovoljan broj kriterijumaa pomoću kojih je ovaj problem opisan. Višekriterijumsko odlučivanje (MCDM) često predstavlja zahtjevan zadatak, jer je neophodno iz skupa alternativa izabrati jednu, na osnovu većeg broja konfliktnih kriterijuma. Pri definisanju energetskog miksa države/lokalne zajednice neohodno je analizirati veći broj međusobno suprostavljenih kriterijuma. U ovom radu prezentovani su kriterijumi i indikatori za opis i ocjenu energetskih sistema za proizvodnju električne i toplotne energije u državi/lokalnoj zajednici: energetska i eksergetska efikasnost, eksergetski faktor, specifični investicioni trošak 1 kW instalisane snage tehnologije, specifični proizvodni trošak po 1 kWh energije, specifična emisija CO2 u kg/kWh, faktor kapaciteta, tehnički vijek trajanja, faktor skladištenja. Prezentovane su i tri metode koje pripadaju MCDM metodama i to su: entropijska (EWM) metoda, metoda Analitičko hijerarhijskog porcesa (AHP) i VIKOR metoda. Metode EWM i AHP korištene su za određivanje težina kriterijuma u uporednim odnosima u smislu tačnosti i konvergencije njihovih izračunatih numeričkih vrijednosti, dok je metoda VIKOR korištenja u procesu optimizacije energetskog miksa.